A spokeswoman for the zoo said the incident was being reviewed internally.

It is understood the health and safety standards around the African Savanna enclosure for the zoo's southern white rhinos are being examined.

One of the photos of the incident on Saturday afternoon was taken by architect Ciaran Ferrie, who posted it to Twitter and said: "Just a child inside the rhino enclosure at @dublinzoo."

The youngster is less than a yard from the fence and can be seen standing on large boulders which act as an additional barricade several feet above the ground.

The adult can be seen taking photos of him while passers-by take pictures of the two of them.

Dublin Zoo has experienced a number of incidents involving its animals down the years, including a teenager from Belfast who was attacked by an Amur tiger in 2006 after scaling two fences and reaching her arm in through a third fence.

In 2010 a penguin was stolen in a suspected prank and in 2008 an orangutan escaped from its enclosure while a school tour was walking by.

Dublin Zoo is expected to reveal a further response to the latest incident in the coming days.